Shigellosis is a global human health problem [1] known to cause diarrheal disease and death in a certain proportion of affected individuals. Shigellosis is primarily a disease of poor, crowded communities that do not have adequate sanitation or clean water. [2] Among the four Shigella sp., Shigella flexneri is the most commonly isolated species in the developing world.

Antimicrobial agents are the main stay of therapy of all cases of shigellosis. However, Shigella sp. have been progressively acquiring resistance to several antimicrobial agents used for the treatment of infections caused by these bacteria. [3] Also, the emergence of multidrug-resistant (MDR) strains of Shigella is a growing concern across the globe.[4] In such a scenario, third-generation cephalosporins are increasingly being used for treating infections caused by MDR Shigella. [5] This in turn has led to the emergence of extended spectrum beta-lactamases (ESBL) producing Shigella sp. Very few reports are available on ESBL producing Shigella from some countries, although there are various studies on MDR strains. Here we report from North India the presence of ESBL production in clinical isolates of MDR Shigella.

A 2-year study was undertaken in a tertiary care center from 1st Jan 2007 to 31st December 2008 to study the prevalence of shigellosis, the common species isolated and the antibiotic susceptibility patterns of the isolates. Isolates found resistant to at least two third-generation cephalosporins were tested for the production of ESBLs by three different phenotypic methods. All stool specimens were processed using standard microbiological procedures, and isolates morphologically resembling Shigella sp. were biochemically tested and confirmed using species-specific antisera (Denka Seiken, Tokyo, Japan).

In 2007, 15 S. flexneri strains and 9 S. boydii strains were biochemically and antigenically confirmed. The antibiotic susceptibility patterns of these isolates are shown in [Table 1]. Of these isolates, one S. flexneri isolate and two S. boydii isolates were found to be resistant to ceftriaxone, cefotaxime, and ceftazidime and were tested for the production of ESBLs by the CLSI recommended method of combination disc technique using cefotaxime and ceftazidime discs alone and in combination with clavulanic acid. [6] These isolates were also tested by the double disc-diffusion synergy test [7] and confirmed by the ESBL Etest strips [8] (AB Biodisk, Solna, Sweden). All the three isolates were found to be positive for ESBL production.

In 2008, of 27 Shigella strains isolated (22 S. flexneri, 3 S. boydii, and 2 S. sonnei) two S. flexneri isolates were found to be ESBL producers - one from the adult age group and one from the pediatric population. The susceptibility pattern is shown in [Table 1].

The study showed Shigella sp. with different susceptibility patterns to a variety of antibiotics. Highest resistance was seen against three of the commonly used antimicrobials such as cotrimoxazole (72.59%), ampicillin (58.82%), and ciprofloxacin (17.64%). These findings are similar to those of an ethiopian study [9] on resistance patterns of Shigella isolates, though our ciprofloxacin resistance is slightly higher, theirs being 9.9%. Resistance to cephalosporins was 16.6% in S. boydii and 8.1% in S. flexneri. Classes of antibiotics such as amikacin, netilmycin, imipenem, and piperacillin/tazobactam showed 100% sensitivity.

ESBLs continue to be a major problem in clinical setups the world over conferring resistance to the expanded spectrum cephalosporins. The high prevalence of ESBLs among Escherichia More Details coli, Klebsiella sp., and Enterobacter sp. has been well documented; however, there are only few cases or small case series of ESBL producing Shigella which have been reported from certain countries. [3] In our study, the total ESBL prevalence over the 2-year period was found to be 8.7% in Shigella sp.

ESBL producing MDR Shigella sp. can arise as an important threat in the treatment of dysentery. Specific guidelines are required for rational use of antibiotics in the treatment of dysentery due to ESBL producing Shigella sp . An outbreak of shigellosis by such strains or the widespread dissemination of these resistant strains in overcrowded communities will prove to be a tough challenge in the containement of the disease. Constant surveillance of the emergence of resistance is highly recommended.